Detector circuit



` Nov. 2, 1937. R, URTEL 2,097,902

DETECTOR C IRCUIT Filed June 1, 1953 Iig, z

INVENTOR eL/00u' UerEL Wwm/ ATTO R N EY Patented Nov. 2, 1937 PATENTOFFICE DETECTOR CIRCUIT Rudolf Urtel, Berlin, Germany, assignor toTelefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin,Germany, a corporation of Germany Application June 1, 1933, Serial No.673,877 In Germany June 2, 1932 4 Claims.

The present invention relates broadly to detector circuits and moreparticularly to detector circuits of the type utilizing gridrectification. It is one of the features of the present invention thatscreen grid type tubes are utilized in the detector circuits the screenelement or which is used for the purpose of controlling certaincharacteristics of the tube.

The objects of the invention will be apparent from a reading of thefollowing specication in connection with the accompanying drawing,wherein,

Figures 1 and 3 show Various curve sheets utilized in explaining theprinciples underlying the invention; and,

Figures 2 and 4 show various preferred embodiments of the invention.

The characteristic feature of grid rectification resides in the factthat with an increase of the amplitude of the carrier frequency theaverage voltage at the grid-condenser increases particularly in suchmanner that the grid potential moves into the negative region wherebythe anode current decreases. The increase of the amplitude of the highfrequency however is limited in that anode rectification begins when thenegative bias is too highgso that an increase of the anode currentoccurs as indicated in Figure 1. The simultaneous occurrence of gridandanode-rectificaticn means distortion of the produced audio frequency. InView of the greater sensitivity of grid-rectification, it is inparticular desirable to increase the range of control. This canobviously be accomplished by using higher voltages i. e. larger zerocurrents. However their choice is Very limited in view of thelimitations in construction.

If for instance a screen grid tube is used as a demodulator, and iffurthermore care is taken that at a higher negative bias the screen gridpotential increases, (Figure 2), a compensation effect is obtained withthe result that a considerably slower decrease of the anode currenttakes place than would be the case without compensating arrangement, inother words, at increasing negative bias the characteristic. again movesfurther towards the left, whereby the range of control increases. Thusit is possible in this manner to apply at the same operating currents ashitherto used, considerably greater amplitudes of the high frequency tothe grid before additionalanode rectification occurs (Figure 3).

A special case of using a compensating circuit is presented by theso-called Wunderlich tube, see Electronics, April 1932 (Figure 4).Hereby (Cl. Z-27) it is however not intended to avoid occurrence ofanode rectication, since this is from the beginning already avoided tc avery great extent due to the special construction of this tube and it israther here the question of preventing ex- Vcess control at audiofrequency. One could be inclined to consider to use a grid rectifiersuited for great amplitudes, directly as end tube, however the fact isthat by increasing the amplitude of the high frequency, the controllableanode current at audio frequency becomes smaller.

In using the above described compensating circuit it is possible tomaintain the anode current nearly constant for any incident amplitudesof the high frequency and thus be able to control nearly the full anodecurrent also for the highest carrier frequencies.

I claim:

1. In the operation of a screen-grid tube grid circuit detector, themethod of maintaining the steady component of the plate current iiowsubstantially uniform despite variations in the strength of carrierenergy applied to the input of the detector which comprises utilizingthe variations in steady component of the plate current due tovariations in the strength of the carrier energy to proportionately andin an opposite sense vary the screen grid voltage.

2. In the operation of a screen-grid detector circuit as a grid circuitdetector, the method of preventing plate rectification within certainextended limits of operation of the detector which comprises producingin the plate circuit a voltage drop proportional to the ow of the steadycomponent of the plate current therethrough and utilizing the producedpotential drop to aifect the screen grid potential.

3. In a screen grid tube detector circuit arranged fcr grid-detection, asource of plate current and a circuit including said source and animpedance device in series connected from the cathode to the anode ofsaid tube, a connection including a resistor element connected acrosssaid series source and impedance device sothat a series closed circuitis formed comprising the source, the impedance device and the resistanceelement, and a connection from the screen grid of the tube to a pointintermediate the resistance element whereby the screen grid potential iscaused to vary as the flow of plate current of the tube varies throughthe impedance element.

4. In a detecting circuit of the type including two signal gridsconnected so as to produce a radio frequency push-pull input circuit inconnection with the cathode and an anode connected in connection Withthe cathode so as to produce a normal audio frequency output circuit, ashielding electrode for said tube, a source of plate cur- Y rent and acircuit including said source and an comprising the source, theimpedance device and the resistance element, and a connection from theshielding electrode of the tube to a point intermediate the resistanceelement and arranged so that the screen grid potential is caused to vary5 as the ow of plate current of the tube varies through the impedanceelement.

RUDOLF U'RTEL. l

